1. Field of the Invention
The present invention relates to a method for manfacturing a semiconductor device, and more particularly, to a method for manfacturing a contact structure.
2. Description of the Related Art
As semiconductor devices bye been become more finely structured, connection layers (or wiring layers) have also become finer. Simultaneously, a contact structure for connecting a connection layer to another connection layer or to a semiconductor substrate has also become finer.
In a first prior art method for manufacturing a contact structure (see: M. Fukumoto et al., "Double Self-aligned Contact Technology for Shielded Bit line Type Stacked Capacitor Cell of 16 MDRAM", IEICE Transactions, Vol, E74, No. 4, pp. 818-826, April 1991), a first connection layer is formed on a first insulating layer formed on a semiconductor substrate. Then, a second insulating layer is formed on the first connection layer, and a contact hole is perforated in the first and second insulating layers. Then, a sidewall insulating layer is formed on sidewalls within the contact hole. Finally, a second connection layer is buried in the contact hole. Thus, the first connection layer is electrically isolated from the second connection layer by the second insulating layer and the sidewall insulating layer. This will be explained later in detail.
In the first prior art method, however, when the pitch of the first connection layer becomes small, the first connection layer may be exposed, since the sidewall insulating layer on the top of the first connection layer is etched. As a result, the first connection layer is short-circuited to the second connection layer.
In a second prior art method for manufacturing a contact structure (see: T. Fukasa et al., "A Margin-Free Contact Process Using An Al.sub.2 O.sub.3 Etch-Stop Layer For High Density Devices", IEDM Tech. Dig., pp. 837-840, 1992), a first connection layer and an Al.sub.2 O.sub.3 cap layer are formed on a first insulating layer formed on a semiconductor substrate. Then, the Al.sub.2 O.sub.3 cap layer and the first connection layer are sequentially patterned, so that the Al.sub.2 O.sub.3 cap layer is formed on only the top of the first connection layer. Further, an Al.sub.2 O.sub.3 layer is formed on the entire surface, and is etched back so that the Al.sub.2 O.sub.3 layer is left on sidewalls of the first connection layer. Then, a second insulating layer is formed, and a contact hole is perforated in the first and second insulating layers. Finally, a second connection layer is buried in the contact hole. Thus, when the Al.sub.2 O.sub.3 layer is left on the sidewalls of the first connection layer by back etching, the first connection layer is hardly exposed, since the Al.sub.2 O.sub.3 cap layer and the Al.sub.2 O.sub.3 layer cover the top of the first connection layer. This will be explained later in detail.
In the second prior art method, however, the second insulating layer is made of boron glass including silicon oxide or boron-including phospho-silicated glass (BPSG). As a result, when a heating operation is carried out to reflow the second insulating layer, the Al.sub.2 O.sub.3 cap layer and the Al.sub.2 O.sub.3 layer thermally react with the silicon component or refractory metal component of the first connection layer, to create an aluminum silicon compound or the like. This may cause a short-circuit between the first and second connection layers. Also, the first connection layer is deteriorated.
In a third prior art method for manufacturing a contact structure (see: JP-A-3-106027), a first connection layer is formed on a first insulating layer formed on a semiconductor substrate. Then, a silicon oxide layer and an AlN.sub.x stopper are sequentially formed on the first connection layer. Then, the AlN.sub.x stopper layer, the silicon oxide layer and the first connection layer are patterned. In this case, the first connection layer is overetched. Then, a second insulating layer is formed, and a contact hole is perforated in the first and second insulating layers. In this case, the second insulating layer is left on sidewalls of the first connection layer. Finally, a second connection layer is buried in the contact hole. This will be explained later in detail.
In the above-described third prior art method, however, the silicon oxide layer is indispensible between the AlN.sub.x stopper and the first connection layer, in order to avoid thermal reaction therebetween. As a result, the contact hole is deeper by the height of the silicon oxide layer, which may cause a contact defect. Also, the first connection layer, particularly, an upper portion thereof is overetched, so that the AlN.sub.x stopper and the silicon oxide layer are unstable with the first connection layer. At worst, the AlN.sub.x stopper and the silicon oxide layer are separated from the first connection layer, which also invites a short-circuit between the first and second connection layers.